The present invention relates to an improved apparatus and method for determining whether a suitable data storage cartridge has been inserted into a disk drive, thereby protecting the drive against damage due to the insertion of disk cartridges and foreign objects that are unacceptable for use in the drive.
Removable disk cartridges for storing digital electronic information typically comprise an outer casing or shell that houses a rotatable recording medium, or disk, upon which electronic information can be stored. The cartridge shell often comprises upper and lower halves that are joined together to house the disk. The disk is mounted on a hub that rotates freely within the shell. When the cartridge is inserted into a disk drive, a spindle motor engages the disk hub in order to rotate the disk. The outer shell of the cartridge typically has some form of opening near its forward edge to provide the recording heads of the drive with access to the recording surface of the disk. A shutter or door mechanism is often provided to cover the opening when the cartridge is not in use, thereby preventing dust or other contaminants from entering the cartridge and settling on the recording surface of the disk. The term "disk cartridge," as used in this application, refers to any data storage device, including tape cartridges.
The actuator that carries the recording heads of the disk drive across the recording surface of the disk should not be allowed to move unless the presence of a disk cartridge with an appropriate form factor, i.e., geometry, is detected. Movement of the actuator where a foreign object or a disk with an inappropriate form factor has been inserted will likely damage the drive or corrupt the data stored on the disk. Thus, when a data-storage cartridge is inserted into a drive, it is critical that the type of cartridge be recognized by the drive as a cartridge that is suitable for safe and reliable use in that particular drive. Most removable cartridge drives use cartridges having similar form factors. Additionally, foreign objects are easily inserted into disk drives. Therefore, disk drives that receive removable disk cartridges must have some mechanism for detecting the insertion or presence of a suitable cartridge within the drive. This mechanism must also be able to discriminate between cartridges appropriate for use in the drive, disks which are not suitable for the drive, and foreign objects.
In the prior art, mechanical switches are typically employed to detect the presence of a disk cartridge. Such switches are often positioned such that when a disk cartridge is fully inserted into a drive, the cartridge contacts the switch and thereby produces an indication that the cartridge is present.
Disk detection systems utilizing reflective materials have been developed and patented. For example, U.S. Pat. No. 5,638,228 ("the '228 patent"), which issued on Jun. 10, 1997, discloses such a system. The '228 patent is hereby incorporated by reference. This patent describes a disk cartridge comprising a reflective marker. The patent also describes a disk drive comprising a light emitter and a light detector coupled to an electrical circuit. When the disk cartridge is inserted into the drive, the emitter and detector become optically coupled by via the reflective marker. This coupling causes an increase in the amount of irradiance reaching the detector, which in turn causes a change in the electrical output of the detector.
As described in the '228 patent, the amount of light reflected by a reflector-equipped cartridge is greater than the amount reflected by most other objects. Therefore, by sensing that the light reflected from an object inserted into a disk drive exceeds a predetermined threshold, the detector and electrical circuit can recognize that a disk cartridge with a reflective marker has been inserted. The electronic circuit will permit activation of the drive's read/write heads under these conditions, thereby allowing the drive to interface with the disk cartridge. Conversely, when the intensity of the reflected light does not exceed the predetermined threshold, the electronic circuit interprets this as indication that a suitable data. cartridge is not present in the drive. The electrical circuit will not enable the heads under this condition, thereby preventing the drive from operating.
The emitter/detector described in the '228 patent has proven to be effective in identifying the presence of disks appropriate for use in a particular disk drive. Under certain limited circumstances, however, the '228 design allows activation of the drive in the presence of disks and foreign objects that may damage the drive. Such activation occurs because objects having surface reflectivities similar to or greater than that of a reflector are interpreted by the '228 design as disks appropriate for use in the drive. Hence, there is a need to provide a greater degree of differentiation between disks appropriate for use in a particular drive, and disks and other objects that can damage the drive if inserted.